The present invention generally relates to electro-mechanical switches and energy-storing actuators. In addition, the present invention relates to electro-mechanical switches and energy-storing actuators that can be adapted for use with thermostats.
Electro-mechanical switches are utilized in a variety of industrial, consumer and commercial applications. Certain types of electrical switching applications require a mechanical switch that can operate properly with a slowly-applied, low-actuation force. Such a switch must also be extremely reliable and generate an accurate, repeatable response, while possessing a small actuation differential and/or low energy requirement. These requirements arise perhaps most commonly in applications involving electro-mechanical thermostats, which are utilized for controlling heating and cooling in homes and buildings where coils of standard bimetal strips form the switch actuation elements. For many years this thermostatic switching function has been performed by mercury bulb switch elements.
Due to the environmental concerns associated with the use of mercury, it is anticipated that electro-mechanical switches will eventually replace mercury-based switches. Legislation currently being drafted and passed in a variety of countries, including the United States, is aimed at banning the use of mercury in most consumer-based applications. Thus, non-mercury based switches must be developed to replace such mercury-type switching mechanisms.
Some attempts have been made at replacing mercury-switching devices. For example, so-called xe2x80x9csnap actionxe2x80x9d switches have been designed to address the environmental concerns that mercury bulb switch elements raise. As utilized herein, the term xe2x80x9csnap action switchxe2x80x9d generally refers to a low actuation force switch, which utilizes an internal mechanism to rapidly shift or snap the movable contact from one position to another, thus making or breaking electrical conduction between the movable contact and a fixed contact in response to moving an operating element of the switch, such as a plunger, a lever, a spring, or the like from a first to a second operating position. Typically, these switches require only a few millimeters of movement by the operating element to change the conduction state of the switch.
Such switches can safely and reliably operate at a current level of several amperes using the standard 24 VAC power that thermostats control. However, when actuated by a slowly-applied, low-actuation force such as is provided by a thermostat""s coiled bimetal strip, snap action switches may occasionally hang in a state between the two conducting states, or may switch so slowly between the two conducting states that unacceptable arcing and/or increased temperature can occur when entering the non-conducting state. Either condition gives rise to unacceptable reliability and predictability of operation. Furthermore, these switches frequently have unacceptably large differentials, which means that the position of the operating element at which actuation of the switch to one state occurs differs substantially from the position of the actuation element at which actuation of the switch to the other state occurs. If the differential is too large, then the temperature range that the controlled space experiences is also too large.
Thermostats with electronic components are generally known in the art. An example of an electro-mechanical thermostat that has been utilized in commercial, consumer and industrial applications is the T87 thermostat produced by Honeywell International, Inc. (xe2x80x9cHoneywellxe2x80x9d) of Minneapolis, Minn. An example of the T87 thermostat is disclosed in the publication xe2x80x9cThermostats T87F,xe2x80x9d Form Number 60-2222-2, S.M. Rev. 4-86, which is incorporated herein by reference. Another example of the T87F thermostat is disclosed in the publication xe2x80x9cT87F Universal Thermostat,xe2x80x9d Form Number 60-0830-3, S.M. Rev. 8-93, which is also incorporated herein by reference. The T87F thermostat, in particular, provides temperature control for residential heating, cooling or heating-cooling systems. U.S. Pat. No. 5,262,752, which is incorporated by reference, is an example of an electrical switch assembly that forms the temperature responsive element in a thermostat.
One of the problems encountered in the efficient utilization of many thermostats in use today is the problem of actuating an electro-mechanical switch with a slow-moving actuator, such as a bimetal element, without sacrificing the switch""s electrical life. For example, electro-mechanical thermostats, such as the T87 line of thermostats manufactured by Honeywell, utilize a bimetal element as the temperature-sensing device. In the operation of the thermostat, the bimetal element moves a small amount at a slow rate. Actuating a switch directly off the bimetal element results in an inordinate amount of time spent, during the switching cycle, at or near snap-over. Electro-mechanical switches have low contact forces near snap-over and zero contact forces at snap-over. When the switch contact forces are low or zero, the amount of electrical resistance at the contact interface increases. As the electrical resistance to current passing through the switch increases, the heat also increases. The electrical life of an electro-mechanical switch is reduced with time as the current is carried at or near the snap-over points.
The present inventors have thus concluded, based on the foregoing, that a need exists for an improved apparatus, including a method thereof, for effectively actuating an electro-mechanical switch.
The present invention generally relates to electro-mechanical switches and energy-storing actuators. In addition, the present invention relates to electro-mechanical switches and energy-storing actuators that can be adapted for use with thermostats.
In one aspect, the invention relates to a control device including a ferromagnetic armature configured to move between a first position and a second position, the ferromagnetic armature being biased in the first position, an energy-storing member positioned adjacent the ferromagnetic armature, the energy-storing member being configured to move between an attracting position and a non-attracting position based on a temperature of an environment surrounding the energy-storing member, a magnet coupled to the energy-storing member, and a ferromagnetic backstop. When the energy-storing member is in the non-attracting position, the magnet is positioned adjacent the ferromagnetic backstop and the ferromagnetic backstop holds the magnet and the energy-storing member in the non-attracting position. When the temperature of the environment changes by an actuating amount, the energy-storing member generates a force sufficient to snap from the non-attracting position to the attracting position. When the energy-storing member snaps from the non-attracting to the attracting position, the armature is caused to snap from the first position to the second position, thereby causing the device to transition from a first operating state to a second operating state.
In another aspect, the invention relates to a control device including a switch including a ferromagnetic armature configured to move between a first position, wherein the armature is biased in the first position, and a second position, wherein in the second position the armature actuates a plunger that causes the switch to snap from an open position to a closed position, and an energy-storing member positioned adjacent the ferromagnetic armature, the energy-storing member including a magnet and being configured to move the magnet between an attracting position and a non-attracting position based on a temperature of an environment surrounding the energy-storing member. When the energy-storing member positions the magnet in the attracting position, the magnet causes the armature to snap from the first position to the second position, thereby actuating the plunger and causing the switch to snap from an open position to a closed position.
In yet another aspect, the invention relates to a switching apparatus for a thermostat including a switch including a lever coupled to a ferromagnetic armature configured to move between a first position, wherein the armature is biased in the first position, and a second position, wherein in the second position the armature actuates a plunger that causes the switch to snap from an open position to a closed position, a bimetal member positioned adjacent the ferromagnetic armature, the bimetal member being configured to move between an attracting position and a non-attracting position based on a temperature of an environment surrounding the bimetal member, a magnet mounted on a free end of the bimetal member, a stop positioned between the ferromagnetic armature and the magnet, the stop including a first surface configured to engage the ferromagnetic armature and a second surface configured to engage the magnet, wherein the first surface is positioned to controlan amount of travel of the ferromagnetic armature, and wherein the stop is configured to provide a minimum distance between the magnet and the ferromagnetic armature, and a ferromagnetic backstop. When the bimetal member is in the non-attracting position, the magnet is positioned adjacent the ferromagnetic backstop and the ferromagnetic backstop holds the magnet and the bimetal member in the non-attracting position. When the temperature of the environment changes by an actuating amount, the bimetal member generates a force sufficient to snap from the non-attracting position to the attracting position. When the bimetal member snaps from the non-attracting to the attracting position, the armature is caused to snap from the first position to the second position, thereby actuating the plunger and causing the device to transition from the open position to the closed position.
In another aspect, the invention relates to a method for switching a thermostat from a first state to a second state, the method including: providing a switch including a ferromagnetic armature, the ferromagnetic armature having a first position in which the switch is in a closed position, and a second position in which the switch is in an open position; positioning a free end of a bimetal member including a magnet adjacent to the ferromagnetic armature; allowing the bimetal member and magnet to move towards and attract the ferromagnetic armature as a temperature of an environment surrounding the bimetal member changes, the magnet causing the ferromagnetic armature to snap from the first position to the second position towards the magnet; stopping the magnet prior to the magnet contacting the ferromagnetic armature; and allowing the switch to snap from the closed position to the open position because of the snap of the ferromagnetic armature.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. Figures in the detailed description that follow more particularly exemplify embodiments of the invention. While certain embodiments will be illustrated and described, the invention is not limited to use in such embodiments.